Messages for the health mailboxes are stuck in queue on Exchange Server 2016

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Symptoms

Assume that there are multiple accepted domains configured in a Microsoft Exchange Server 2016 environment. When the default accepted domain isn't the primary SMTP address in the Default Policy email address policy, messages for the health mailboxes are stuck in the Shadow and Outbound SmarHostConnect queues.

Note This issue also occurs in Microsoft Exchange Server 2013, and you can follow the Workaround section to fix the issue for Exchange Server 2013.

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Cause

This issue occurs because the managed availability probe for incoming messages uses the default accepted domain and the health mailboxes don't contain an SMTP address that uses this domain.

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Resolution

To fix this issue, install Cumulative Update 4 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.

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Workaround

To work around this issue in Exchange Server 2013, use one of the following methods:

Method 1

Add the default accepted domain as a secondary SMTP address to the Default Policy email address policy.

For more information, see Edit an email address policy.
Method 2

Change the default accepted domain to match the primary SMTP address in the Default Policy email address policy.

For more information, see Set-AcceptedDomain.

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